Lubricants are used for various purposes such as use in metalworking fluid, engine oil, driving system oils, and working oil, but in recent years, with increased performance and size of machines the viscosity of lubricant oil has been reduced for fuel-saving purposes. The impact of this is that there is an increase in cases where the pressure applied to contact surfaces that require lubrication is grater than here before and there is an increase in problems of wear occurring in the contact surface. In order to prevent such wear, extreme pressure agents are generally used (for example, see Patent publications 1-3).
Patent publication 1 describes sulfides, sulfoxides, sulfones, thiophosphinates, thiocarbonates, dithiocarbides, alkylthiocarbamoyls, fat and oil, sulfurated fat and oil, sulfurated olefins, phosphates, phosphites, phosphoric ester amine salts, phosphorous ester amine salts, chlorinated hydrocarbons, chlorinated fat and oil, zinc dithiophosphates, thiocarbamates, and the like as extreme pressure agents for lubricant oils.
Patent publication 2 describes lead naphthenate, sulfurated fatty acid esters, sulfurated palm oil, sulfurated terpene, dibenzyl disulfide, chlorinated paraffin, chloronaphtha xanthate, tricresyl phosphate, tributyl phosphate, tricresyl phosphite, n-butyldi-n-octyl phosphinate, di-n-butyl dihexyl phosphonate, di-n-butyl phenyl phosphonate, dibutyl phosphoramidate, amine dibutyl phosphate and the like as extreme pressure agents for lubricant oils.
Patent publication 3 describes sulfurated fat and oil, olefin polysulfides, dibenzyl sulfide, monooctyl phosphate, tributyl phosphate, triphenyl phosphite, tributyl phosphite, thiophosphate, thiophosphoric acid metal salts, thiocarbamic acid metal salts, acidic phosphoric acid ester metal salts, and the like as extreme pressure agents for lubricant oils.
However, most of these known extreme pressure agents contain elements such as sulfur, phosphorus, lead, zinc, and chlorine. Although these elements play an important role as extreme pressure agents, on the other hand there are cases where they may lead to corrosion on lubricated surfaces, may adversely affect human health or have an adverse effect on the environment when disposing of lubricant oils. Recently, due to increased awareness of environmental issues and safety regarding humans, use of compounds comprising any of these elements is avoided and there is a strong desire to use compounds consisting of three elements, i.e., carbon, hydrogen, and oxygen are used to achieve the effect. On the other hand, it has been known that fat and oil (see Patent publication 1) and compounds without metal elements or the like such as fatty acid esters have performance as extreme pressure agents, but the level of performance of these compounds as extreme pressure agents is low, and thus they cannot be used under severe conditions. Therefore, a highly safe extreme pressure agent which does not contain any of the above metal elements or the like but which exhibits performance equivalent to that of conventional extreme pressure agents containing a metal element or the like, has been desired.